A new Alexander McCall Smith novel isn't news in a way. The prolific Scottish author is currently writing no fewer than five series of books. However for fans, a new No. 1 Ladies Detective Agency book is a big event.

And for Minnesota fans there's an added extra in the latest book in the series -- a sub-plot about St Paul.

One of the challenges of talking to Alexander McCall Smith about his books is numbers, particularly when it comes to Mma Ramotswe and her No 1 Detective Agency.

"This is the 11th book," says McCall Smith. Then he looks doubtful. "Actually, really, that's...." He stands and calls to his assistant in the next room.

People write to me and say, they are quite direct. And they say: 'Please don't die soon.' That's a very, very nice sort of letter to get.

Alexander McCall Smith

"Lesley? Is this the 11th or the 12th book?"

But McCall Smith's assistant isn't sure either. So he grabs a copy of the latest novel, "The Double Comfort Safari Club" and opens it to list of previous titles.

He quickly gets to 11 and snaps the book shut.

McCall Smith is sitting in his large book lined library on the south side of Edinburgh. The shelves, reach the high ceiling and cover two walls of the large room. It's a quiet and comfortable spot.

This is where McCall Smith writes when he is in Edinburgh.

"I'm told that the general rule in publishing is that you write one book a year, and no more than that," he says. "Well, we are, I am afraid, breaking that in that I am writing either four or five a year."

It takes discipline. He's at his desk at 4 a.m. most mornings. McCall Smith says he starts the year with Isabel Dalhousie novel, from the Sunday Philosophy Club series. Then he moves to writing about Mma Ramotswe's Botswanan detective agency in the summer and early autumn.

In between he writes a 44 Scotland Street novel for the Scotsman newspaper to be published a chapter a day. He does a similar thing online for the Daily Telegraph for his new series Corduroy Mansions. The first of those novels will be published here in July. There is sometimes a diversion to his German Philologist series as well.

Some writers might find this schedule tough, but not McCall Smith.

"I never look upon my annual meeting with Mma Ramotswe and Mr. J.L.B. Matekone, and Mma Makutse as a chore or a duty of any sort," he says. "I look upon it as an opportunity to renew acquaintances."

And fans of the books do as well. McCall Smith's work has been translated into 44 different languages. He's sold in excess of 15 million books. Fans say they are attracted to the gentle human wisdom of the stories. For a detective series there is remarkably little crime in the Mma Ramotswe novels.

McCall Smith travels a lot, and often the places he visits end up in his books. Take "The Double Comfort Safari Club" for example.

"There is a character who comes from St. Paul," he says.

It's a woman who makes a request which launches Mma Ramotswe on an adventure. McCall Smith visited Minnesota a few years back, and it made enough of an impression to warrant a character in a book.

"Now I am not sure why I decided that," he admits. "But I think it is probably due to that fact that I very much like that part of the world."

He says he's frustrated the erupting Icelandic volcano grounded him in April. It forced the cancellation of an entire U.S. tour, including a lecture at the State Theater in Minneapolis. He says his U.S. agents are working to reschedule for the fall. There are no details available but he'd like it to include Minnesota.

For now Alexander McCall Smith says he wants to just continue writing, which will be a comfort to his more fervent fans.

"People write to me and say, they are quite direct. And they say: 'Please don't die soon.' That's a very, very nice sort of letter to get," he says. "If somebody asks you to put off your appointment with mortality, that's very very nice, that's very encouraging. People like to get that sort of message."

"The Double Comfort Safari Club" is available now in hardcover the U.S. "Teatime for the Traditionally Built" -- book 10 of the No. 1 Ladies Detective Agency Series -- is now out in paperback.